Hello Patricio,
It was a close call Patricio, I am sure that on the next attempt you will achieve the MS-900 certification, I will help you as much as I can with your doubt friend.
- Project is a project manager. You can schedule tasks, subtasks and also work dependent tasks. It allows you to see the project in different ways, as it has the grid views, Kanban style task panels and time scale Gantt charts (the most used one perhaps).
- Planner is a task manager, your team will be able to better organize the work in tasks in a very visual way. You will have to structure the work into tasks. On a Kanban board you will assign and manage these tasks; these tasks you add to buckets.
- Booking allows you to manage and schedule appointments. Your customers will be able to make appointments with the booking page that Booking provides, according to your free schedules that you indicate to Booking. It relies heavily on Outlook to work with calendar.
I hope I have helped you, have a great day.
PS: best wishes and success for the next MS-900 exam.